Figure 1

Relative abundances of carrier ([12C]i + [13C]i) and carbon-11 ([11C]i) species in a 11C-labeled tracer: [12C]i 98.9%; [13C]i ~ 1.1%; and [11C]i typically < 0.1%. In this report, LC–MS/MS was used to measure these three species in order to derive the relationship between tracer mass (through activity derived from Avogadro’s number and decay constant) and radioactivity.